Promoting Reversibility of Co‐Free Layered Cathodes by Al and Cation Vacancy

Abstract Li‐ion batteries adopting layered cathodes can effectively alleviate the range limitations of electric vehicles. Unfortunately the scarcity of Co inhibits massive deployment of layered cathodes. Eliminating Co from layered cathodes is necessary to make a breakthrough in global application of electric vehicles. However, Co‐free layered cathodes face challenges in delithiation/lithiation reversibility since Co plays a pivotal role in suppressing Li/Ni mixing. Many metals have been proposed to replace Co in layered cathodes, and sophisticated compositional designs always consider suppressing Li/Ni mixing as the top priority. Here, the authors show that Li/Ni mixing can be suppressed by Al and cation vacancies in different manners; however, irreversible capacities are prominently different given similar Li/Ni mixing. In‐situ X‐ray diffraction monitored potentiostatic‐intermittent‐titration measurements reveal that Al decreases the lattice strain between H2 and H3 phase by 13.6%, but Al has an adverse impact on structure reversibility. While Al and cation vacancies together not only significantly reduce the H2/H3 lattice strain by 78% but also greatly enhance structure reversibility. Furthermore, the first‐principles calculation shows that cation vacancies can remarkably reduce the Li migration energy barrier by an order of magnitude. Reversibility of the newly designed Co‐free cathode is significantly enhanced through the synergic effect of Al and cation vacancies.